Automatic line testing and switching circuits



June 26, 1945. a. DYSART AUTOMATIC LINE TESTING'AND SWITCHING CIRCUIT Filed July 24, 1943 ILARM HOLD Kl? 3 Sheets-Sheet 1 INVENTOR B DYSART B V Maw A TTORNEY June 26, 1945. -r 2,379,069

AUTOMATIC LINE TESTING AND SWITCHING CIRCUIT Filed July 24, 1943 3 Sheets-Sheet 2 MAN LOCK

h UNLOCK FIG. 2

INK/EN r0? B DKSART By J W I-gIIHI ll 5 k E 9,

June 26, 1945. B. DYSART 2,379,069

AUTOMATIC LINE TESTING AND SWITCHING CIRCUIT Filed July 24, 1943 3 Sheets-Sheet 3 P/LDT PILOT OL T- LINE 17C 4ND ALAIN CONTROL CCZ' STATION A '01 (one) INVENTOR a. orsmr ATTORNEY Patented June 26, 1945 AUTOMATIC LINE TESTING AND- SWITCHING CIRCUITS Application July 24, 1943, Serial No. 495,989

17 Claims.

The invention relates to broad-frequency band transmission systems. such as multichannel carrier wave signaling systems, and particularly to automatic circuits for use with such systems to test for line trouble conditions, to indicate abnormal line trouble conditions and to substitute spare lines for lines found defective by such tests.

In such system employed for transmitting sig-- nal waves over long distances, it is customary to use a large number of signal wave repeaters in tandem spaced at intervals which may be as short as five miles, or even less, with a number of unattended auxiliary repeaters located between each two main repeaters which may be located fifty to seventy miles apart, and which may be attended or unattended. The failure or substantial impairment in transmission efiiciency of a single transmission element, for example, an amplifying vacuum tube or conductor in a line section, may result in complete failure of or intolerable degradation of transmission over that line section. In certain carrier wave signaling systems, such as coaxial cable carrier systems, up to five hundred signaling channels may be transmitted over a single line pair or coaxial conductor. It is apparent that complete or partial transmission failure within a repeater section in such a system may effectively interrupt or degrade transmission in hundreds of signaling circuits. resulting in considerable incon venience, loss of time and loss in revenue before the condition causing the trouble can be remedied. It is of great importance, therefore, that means be provided to nullify the effects of such line failures. For this reason, parallel identical lines are provided in each direction so arranged with suitable switching circuits that a spare line section may be substituted in place of a section in which a transmission failure occurs.

In order to facilitate the maintenance of such systems, it is known to continuously transmit over the signal transmission lines between repeater stations one or more pilot waves of different frequencies outside the transmitted signal frequency band but closely adjacent thereto, so that the pilot waves are subjected to substantially the same line conditions as the signals. The deviations of the transmitted pilot waves from normal levels at repeater points are utilized to control indicating apparatus which may be observed to determine if the system is functioning properly, or to control apparatus for automatically regulating the gain of repeaters to compensate for cable variations and counteract changes in repeater gain due to aging of vacuum tubes, etc. in preceding repeater sections. It is also known to employ one or more of the transmitted pilot waves separately to selectively control the operation of special relay circuits to actuate alarms at attended repeater stations when the pilot levels thereat deviate in either direction a given amount from a predetermined value indicating line failure or other serious line trouble; and to utilize corresponding excessive deviations in the level of a single pilot wave to control the operation of switching arrangements at attended and unattended repeater stations to effectively transfer signal transmission in preceding repeater sections, comprising a switching section, from the working line which has become defective to a spare line.

An object of the invention is to improve such automatic line trouble alarm and switching arrangements.

A related object is to automatically detect line trouble conditions in the repeater sections of a long-distance signal wave transmission system, and to automatically substitute spare line sections for working line sections which have become defective.

A more specific object is to continuously monitor the working and spare lines in the repeater sections of a broad-frequency band repeatered signaling system to determine when they have failed completely or partially, and when this occurs in a working line, to automatically switch signal transmission to a good" spare line; to indicate which of the lines are working and which are spare, and the condition of such lines; and to operate appropriate line trouble alarms for the failed line or lines.

The above objects are attained in accordance with the invention by automatic circuit arrangements combining the functions of the separate pilot-controlled alarm circuits and pilot-controlled line switching circuits of the prior art systems referred to above, in such manner as to provide improved operation under all conditions of service with economy of apparatus.

In one embodiment, the circuit arrangement of the invention comprises a single chain of relays at main switching repeater points of such a system, adapted for automatic control through selective amplifler-rectifler-relay circuits bridged across the outputs of the working and spare lines in the preceding switching section, by any one of a plurality of pilot waves of different frequencies continuously transmitted over each of the lines, to continuously monitor each line for 2 as'zaoeo encessivelinetroubie;tooperats ts toprovidethroughsignsltransnnmionwillbe alarm'sincaseoiexcessivetroublesinanyoi reierredtoasa"working"line,andtheother thelineszandtotransler signaltransparaliellineinsuchaswitchingsectiomnotso missiontromtheworkinglinetotbesparcline connected,willbereiermdtoasthe"spare teristi mission scribed The various l 'ig. 3 shows oi circuit ts inventiontoasimilarsignaltrannnissionsystem employing two working lines and a common spare lineioreachdirectionoisignaltransmisslon.

Although the invention Ls adapted for use with any broad-frequency band signal transmission system employing any type oi line. it is articularly applicable to and will be described in connection with a two-way multichannel coaxial cable carrier wave signaling system employing a type of line structure comprising a tubular conductor within which a central conductor or wire is mounted coaxially by means of insulating supports, commonly referred to as a coaxial or a "coaxial pair." and in which a number these coaxialpairsrespectivelyservingasworkingand spare lines between repeater stations are contained within a common outer tubular conductor to form what is known as a coaxial cable.

The particular coaxial system to be described for which the arrangements oi the invention were devised operates on a i'our-wirc basis, transmission in opposite directions being eiiected on separate cable pairs. Two coaxial line pairs, one regular and one alternate. are provided in each switching section for each direction oi transmission. both being completely q pp with transmitting and receiving amplifiers and associated regulating circuits. The repeaters in the particular system to be described are arranged to handle a band of frequencies adequate for 480 telephone channels in each direction. requiring a total band of frequencies extendin up to 2 megacycles, or one television circuit requiring a total band of frequencies extending up to 8 megacycles. The system includes a number of main repeaters located approximately nity miles apart and between them a number oi auxiliary unattended repeaters spaced at approximately Bill-mile intervals. Certain oi the main repeaters. known as "switching main repeaters and the terminal repeaters are so constituted as to provide switching facilities so that on may be switched from the regular to alternate lines, or vice versa, depending which lines are then working and spare lines in the preceding switching section.

In the following description 0! the circuits of the invention in conjunction with the drawings, the line section between each two successive main switching repeater stations. or between a terminal repeater station and the next adiacent main switching repeater station. will be referred to as a switching section. Each line in each switching section which is operatively connected line.

Fig.1 shows adiacent switching sections rm. MB for the west-to-east and east-to-west directions oi waycoaxialearriertelcphonesystemsuchas described above. which is equipped with pilotcontrolled line testing. alarm and switching circuits in accordance with the invention. The repeater section MB for the west-to-east ing section, which is fully equipped with a transmitting amplifier rm and receiving amplifier HA1. and with associated gain regulating and equalizing apparatus (not shown); an equivalent alternate coaxial pair, to be referred to hereinafter as has LB. including the transmitting ampiinerrsaandthereceivingampliilerltliaextending between the same stations; coaxislpaintobereierredtohereinaiteras the working output line Cid. at the output oi the switching section, having its output permanentlyeonnectcdtotheinwtoithenext switching section and its input adapted for connectioneithertotheoutputoithelinemorto the output of the alternate line 18; and a secondcoaxialpairSLattheoutputoitheline switching section having its output permanently connected to the termination TN; and its input adapted for connection either to the output oi the line LA or to the output of the line LB, whichever is operating as the spare line.

'I'heinputsoithelinesmandtheminthe switching section MR are tly connected the hybrid repeating coil H01 tion with the output (working) line Clo oi the preceding switching section. so as to be supplied in common irom the latter line with equal energy portions of the carrier signal irequency band containingthecarriersignalsoiallsignalchannels to be transmitted.

If the switching section MR contains the first main repeater section in the system ior transmission in the west-to-east direction so that the hybridcoilHCiislocatedataterminflr-epeater station, pilot waves of the irequencies 6i kilocycles and 2064 kllocycles on either side of the carrier signal band to be transmitted, and oi equal, initially constant amplitude levels. are continuously supplied in common to the inputs of the lines LA and LB through that hybrid coil from the combined output oi the pilot wave sources P1 and Pa generating these we connected to its net side. In that output impedance of the two pilotwavescurcesriandl'swmddbemadc such so that it operates as an equivalent line balancing network to balance the characteristi impedanccoitheincominglineclewhichit laces. through the hybrid coil 801. The pilot waves could, oi course, be supplied in similar manner at any succeeding main switching point in the system. if desired.

All of the apparatus shown to the right or the dot-dash line x-x is assumed to be located at the switching repeater station at the output of the switching section MR.

Between repeater stations. the (our coaxial pairs, including one regular and one alternate pair of each direction of transmission, are preferably contained within one coaxial cable (not shown).

Included among the circuits at the switching repeater station at the output end of the switching section MR, is the line switching circuit US, including the switching relays BR, AR, BA and AA. shown within the dot-dash box so labeled. The function of the line switching circuit L8 is to transfer the connections between the line LA or the alternate line LB and the output line CLl, so as to provide through transmission of signals and pilot waves to the following switching section of the system by either alternate line, as required.

When the line LA oi the repeater section MR is used as a working line, the relays within tl-e line switching circuit LS are in their normal unoperated condition. Then, the inner conductor I of the incoming coaxial line LA is connected to the inner conductor 2 of the output coaxial line CL: through the normally closed contacts of the relay BR. This completes the transmission path for the carrier signals and the pilot waves over the switching section MR to tl-e next switching section by way of lines LA and CL]. The normally open contacts of the relay AR open the circuit between the line LA and the output coaxial pair SL eventually terminated in the 72-ohm resistance network TNl. The connection of inner conductor 5 oi the line LE to the inner conductor 2 of output line CL, is opened by the normally open contacts of the relay BA, thus normally preventing transmission from the line L3 to the output line GL1. The normally closed contacts of the rela AA complete a connection through the output circuit SL of the terminating network TNl. across tle output of line LB. When the relays BR, AR, BA and AA in the line switching circuit 1.8 are in the operated condition, the connections are reversed so that signal transmission is obtained between the alternate line LB. which is now the working line, and the output line 0L1. and the terminating network TN]. is disconnected from the output of line LB and is connected across the output of the regular line LA which now operates as the spare line.

The relay OP in the line switching circuit LS is provided to control the operation of the line switch relays. AR. AA, BR, BA, so as to prevent any loss in signal transmission over the repeater section during the period in which through signal transmission is being transferred from the line LA operating as the working line to the alternate line LB operating as the spare line, or

from the alternate line LB operating as the working line to the line LA operating as the spare line. Tris is accomplished by a make-make spring contact combination of the relay 0? which insures that the relays AR and BA operate before the relays BR and AA operate; also that the relays BR and AA will release before the relays AR and BA will release. This means that for a short interval during both the operate and release time of the switching relay controlling the line switching circuit LS. both the line LA and tie alternate line LB will be connected to the outgoing line CL; before the line being switched out of service is disconnected.

The line switching circuit LS in accordance with the invention is controlled by the line switch and alarm control circuit LSC comprising the chain of relays and associated elements illustrated in detail in Fig. 2. The circuit LBC, in turn, is adapted for control by either or both or the 64-kilocycle or 2064-kilocycle working line "pilot voltmeters PVi and PV: respectively, bridged across the output line 0111, and therefore across the output of the particular line LA cr LB. operating as the "working" line; and by either or both the 64-kiloeycle or 2064-kllocycle spare line "pilot voltmeters" PVJ and PV; respectively, bridged across the output circuit SL leading to the terminating network TM, and therefore across the output of the particular line, LB or LA, operating as the spare for the other operating as the "working" line. Each pilot voltmeter has a high impedance input so as to cause negligible loss in the associated transmission line. The pilot voltmeters PVi and PV: respectively. include in their inputs, filters PF], PFs, each adapted for selecting from the associated "working or "spare" line a portion of the energy of the received 64-kilocycle pilot wave; amplifierrectifiers ARl, AR: respectively, for amplifying and rectifying the pilot energy selected by the associated filter; and sensitive switching relays SR1, SR: having an operating coil supplied with the rectified pilot energy from the output oi amplifier-rectifiers AR: and AR: respectively. In addition to the operating coil each sensitive switching relay SR1, SR: includes two stationary contacts, a movable contact arm or needle designed to be maintained in a neutral position between the two contacts when the level of the rectified pilot energy supplied to the operating coil is within predetermined tolerable limits indicating satisfactor transmission conditions in the associated line, and to be operated to one contact or the other under control of the operating coil when the level of the rectified 64-kilocycle pilot energy supplied thereto becomes greater or less, respectively. than the average normal value by a given amount, say 5 decibels. indicating failure of or excessive degradation in transmission over the associated line; and a restoring or reset coil adapted for returning the relay armature to the neutral position when energized by direct current from an associated battery by the application of a ground to the lead r under control of the line switch control circuit LSC.

Similarly, the pilot voltmeters PVz, PV4 respcctively, include in their input a filter PF'Z, PF4 [or selecting a portion of the energy of the received 2064-ki1ocycie pilot waves from the associated working" or "spare" line; amplifierrectiilers ARz, AR; for amplifying and rectifying the selected 2064-kilocycle pilot energy; and a sensitive switching relay SR2. SR4. identical with the relays SR: and SR3, controlled by the rectified pilot energy applied to its operating coil, operating to cause the relay armature to be operated to one or the other of the stationary rclay contacts when the level of that energy varies 1-5 decibels from the average normal value; and to return the movable armature to its neutral position when an operating ground is supplied to its restoring or reset coil over the lead 1' under control of the line switch control circuit [50. When the armature of the switching relay of any one of the pilot voltmeters is moved to either of the relay contacts. an operating ground is supplied to one of the leads 0 (c1 or 02) of the associated line switching and alarm control circuit 18C.

The adjacent switching section MR for the east-to-west direction of transmission includes elements similar to those described above for the oppositely-directed switching section MR, as

indicated by the use of the same characters ior identifying corresponding elementehut followed hyaprimet') marklnthecaseoiswltchingsectionlm'. 'lheoperationoitheo! the invention in conmction with the switching section MB for the east-to-west direction of will be understood therefore from the lollowing detailed description in connection witlil 'igaland'soitheoperationotthecorrespending circuitarrangementsassoclatcdwiththe switching section HR for the west-to-east directionoion.

Dsscarrnon or OPIRAIIOII General Ifnoline troubleeidstsonthesystempreceding thelineswitchingpointshowntotherightotthe dot-dash line XX', the deviation in the iii-kilocycle and 2064-kilocycle pilot levels from normal levels at that point will be insufllcient to cause operation oi the (SR) switching relays in the corresponding pilot voitmeters associated with the working and spare lines, and the movable armatures of those switching relays will be maintained at their normal mid-scale operating positions. Under these conditions, no operating grounds are supplied by those relays over the leads to the line switch control circuit 1.80. The relays A, B, C,DandG inthelattercircultaretheninthe released condition, and the relay B is held operated through contacts on the relay G. I! the relay E is released. the relay DP and thus the associated line switching relays AR, BR, BA and AA in the line switching circuit LS are also released, and the switching section is working on line LA. If the relay 1! is operated by application oi groundtothe leadcl causingtheoperationflrst otrelayAand thenotrelayDtoapplyanoperating ground to the winding 0! relay B. it is locked operated through contacts on the released relay C. This lock-up ground is also applied in parallel with the winding of relay E to the winding of the relay 0?, which locks the latter relay operated. 'I'hisinturn locksthellneswitching rcleysinthe line switching circuit LS operated. which results in the shifting o1 transmission over the swtiching section HR to the alternate line LB.

Ii a line trouble occurs in one or both of the lines, LA and LB, preceding the switching point at the output of the switching section MR, which trouble is sutflcient to cause the level of the 64- kilocyle or 2064-kilocycle pilot wave, or both. transmitted over the respective lines, to drop or rise 5 decibels from normal, the (SR) switching relay or relays in the corresponding pilot voltmeters associated with the output of that line or lines will operate. This will cause a ground or grounds to be supplied over the cl or (:2 lead, or both, to the line switch and alarm control circuit [SC to cause corresponding operation of that circuit, which may or may not result in a line switch, depending on which pilot voltmeter switching relay or relays become operated.

It the spare line fails and the working line remains good, so that either one or both of the (SB) relays in the 64-kiiocycle and .lilfii-kilocycle pilot voltmeter-s associated with the spare line become operated, sampling (periodic resetting of the armatures oi the operated switching relays to the neutral position by periodic application of energizinggioundtotheirrestoringresetcoilsthrough the common lead 1' under control of the line switch control circuit L50) will occur and a SP rail alarm willresultuntil thelinetroubleiscleared.

asvaoee Iitheworkinglinelailnandthesparelinsremainsgood.sothateltherone,orhoth,o!the switchingrelays(8lt) intheM-kllocycleand m-kilocycle pilot voltmeter: associated with the working line become operated, the line switching circuit 1.8 will operate under control oi circuit 180 to cause an immediate switch which interchanges the o! the received lines LA andI-B,sothattheworkingiineisrestoredand thesparelineistheialledline,andanswslarm will occur. Also, that is, periodic resettingoltheswitchingrelaysofthei'ailedline pilot voltmeters, will ensue imder control 0! the lineswitchingandalarmcontroicircuitmcuntil the line trouble iscleared.

Ii'bothwortlngandsparelinestailsothatany one, or both, of the (SR) relays in the 84-kilocycle and 2064-kilocycle pilot voltmeters associated with each oi the working and spare lines, become operated,thelineswltchandcontrolcircuitLSCwill cause sampling of the (SR) relays in the .pilot voltmeters associated with both tailed lines, and a total fall alarm will result until the line trouble is cleared. When the trouble clears up on either line, the switching unit functions to restore service on that cleared line.

Spore line failure line switch and alarm control circuit 180 to be operated. The operation oi the relay G applies operating ground to the winding of relay A, which is a slow-acting relay; disconnects 24-volts from the winding of the relay H, which is normally 40 operated; connects the winding of the relay J to contactltoi'therelayli; andopensthepulse sender circuit (that portion of the line switch control circuit LSC over which the pulse, applied by operation of either working line pilot voltmeter switching relay or the manual switch keys, is sent and repeated over lead a to the line switchin: circuit LS causing it to function). The disconnection of 24-volts from the winding of the relay H causes the immediate release of that relay. The release oi the relay It applies ground to the winding of the relay J which is slow-acting, and applies ground to the winding of the relay C or D, depending on whether the relay E is released or operated, respectively. The relay E is releasedwhentheregularlinemis the working line, and is operated when the alternate line LB is the working line. The relay C or D then operates immediately.

The slow-acting relay A flnaltv operates. The operation oi this relay connects one lilo-microiarad section of condenser C1 in series with other circuit elements to its winding; connects a lockup ground to the operated relay C or D; a plies ground through operated contacts on the relay 0 or D, and through released contacts on the relay 1'' to the reset windings of the four switching relays SR1 to BBQ in the pilot voltmeters PVi to Pv inpsrallelthroughcommonleadr: endanplies ground to the pulse sender circuit (defined above), which was previously opened by operation of the relay G.

The operating ground applied to the reset windings of the switching relays SR1 and SR4 operates their reset mechanisms to restore the contact arm or needle 01' those relays to their initial neutral position, which removes the ground connection applied by operation or the spare line switching relaysSRa and SR... over lead cl to th winding oi the relay G, causing the latter relay to release. The release of the relay G removes operating ground from the winding of the relay A; connects -24-volts to the winding of the relay H; closes the pulse sender circuit: and disconnects ground from the winding of the relay J.

The removal of the ground from th winding the relay A does not immediately release that relay, due to the previous connection oi the 100- microfarad section 01' condenser C1 to its winding. The connection of 24-V0lts to the winding of the relay H operates that relay. The closing of the pulse sender circuit does nothing due to the previous operation of the relay C or D. The removal of ground from the winding oi relay J rel ases that relay.

The operation 01' the relay H applies ground through now operated contacts on the relay C or D to the winding of the relay B. The ground applied to the winding of relay B operates that relay, which connects one 200-microiarad section of the Ca condenser (plus the other sections thereoi if the slow sampling key is operated) to the winding of the now operated relay H; transfers the working line pilot switching relay connection via. the corresponding 0 lead from the winding of the relay A to the major total fail alarm circuit, which involves the relays J, K, R and L; transfers the now grounded pulse sender circuit from the contacts of the relay E to the winding of the relay J causing operation of that relay; removes a short circuit from the windin of t e relay and closes the spare fail alarm circuit, which involves the relay N, so that it may now respond to the following conditions:

After approximately two seconds from the time the ground was removed from the winding of the slow-acting relay A, that relay releases. Its release removes the ground through the common lead r from the reset windings of the tour pilot voltmeter switching relays 8R1 to SR0; removes the lock-up ground from the winding of the operated relay C or D; removes the ground from the pulse sender circuit; and prepares the total fail alarm circuit for operation, if required by line conditions, by operating the relay K, as will be described later under "Total iailure."

The operated relay C or D and the reset mechanism of the pilot voltmeter switching relays SR1 to SR4 are then released. The release of the relay C or D removes the ground from the winding of the relay B, which will remain operated for approximately three seconds longer due to the charging of the 100-microfarad section of condenser Ci through its operating winding. The

release of the reset mechanisms 01' the pilot voltmeter switching relays permits continued spare line failure to again operate the switching relays oi the pilot voltmeters associated with that line. The subsequent operation of the spare line pilot voltmeter switching relays again applies ground to the winding 0! the relay G. which operates.

The operation of the relay G applies ground to the winding 01' relay A: applies a lock-up ground to the winding of the relay B; disconnects -24- volts from the winding of the relay H: opens the pulse sender circuit, which releases the relay J in approximately one-tenth of a second, the time required for the associated liw-microfarad section oi condenser 01 to discharge through its winding, which in turn releases the relay K; connects the winding oi the relay J to terminal 8t 01 the relay H; and applies a ground through now perated contacts on the relay E, through norma ly released contacts on the relay L to the winding of the relay N, and through normally released contacts on relay M to the 8? tall lamp, which lights up to indicate that the spare line is still defective.

The relay N operates immediately with the application of the ground to its winding. and locks operated, applying operating grounds to the associated minor oince alarm, which includes an audible alarm and an annunciator lamp (not shown). The ground applied to the minor audible alarm and the lock-up ground on the relay N are derived separately through normally released contacts on the relays L and 8. The slow-acting relay A finall operates, setting up conditions so that the circuit for resetting the pilot voltmeter switching relays will operate as soon as the relay C or D becomes operated.

In approximately eight seconds or more if the slow sampling key is operated after the operation of the relay G, the H relay releases. The H relay is held operated for that period by the C: condenser section or sections connected to its winding in the previous operation of the relay B. The holding time oi the relay 1! is increased approximately 12 seconds for each 200 microi'arad section or the condenser C: connected to its winding.

The release 01' the relay H again operates the relay C or D, as previously described, which looks operated to the relay A, and operates all the pilot voltmeter switching relay reset mechanisms by applying operating grounds to their reset windings.

The above-described sampling process will be repeated periodically until the spare line failure is cleared or the circuit is manually locked.

When the spare line trouble has been cleared, the next subsequent reset or the associated pilot voltmeter switching relays will permanently restore them to the unoperated condition. The relay G will then remain in the non-operated condition, so that the lock-up ground will not be applied to the winding of the relay B. In approximately two seconds aiter completion of the reset or the pilot voltmeter switching relays, the relay B will release to restore the circuit to normal. The slow release of the relay B is due to the connection of the IOO-microfarad condenser or to its winding.

Working line failure A working line failure causes the operation of one or both of the pilot voltmeter switching relays associated with that line, which causes ground to be applied over the corresponding c lead, through contacts on time relay B, to the winding 01' the relay A causing the latter relay to operate. The operation of relay A applies a ground to the pulse sender circuit via released contacts on the relay K, released contacts on the relay G, released contacts on the relay B, released contacts on the relay J, through contacts on the relay E to the winding oi the relay D or C, depending on whether the relay E is released or operated, respectively.

The operation of the relay D applies ground to the lead a of the line switching circuit 18 causing operation of the relay OP which, in the manner which has been previously described, causes a switch from the regular line to the alternate or spare line. At the same time, the relarll, which is slow-acting, is operated and locked up on ground from the relay C. The operation of the relay C, on the other hand, removes the ground which looks operated the relay E and line switch relay releasing the relay]: and line switching oncuit LB, which in turn causes a switch from the alternate line back to the regular line. The operated relay C or D locks operated to the operated relay A.

The operation of the relay C or D passes a ground from the operated relay H to the winding of the relay B, causing the relay B to operate, and also passes a ground irom the operated-relay A through released contacts on the relay 1" and common lead r to the pilot voltmeter switchins relay reset windings, causing the reset mechanism of these relays to operate. The operation or the relay 3 transfers the grounded pulse sender circuit to the winding oi the relay J, causing the subsequent operation of that relay and relay K, as described above under "Spare line failure."

The ground on the pulse sender circuit. which causes the operation of the relay C or D, passes through contacts on the relay E and through normally made contacts on the MAN-SW key to the winding of the relay P. Alter the relay C or D becomes operated, the lock-up ground tor the operated C or D relay, which is derived from the operated relay A, is paralleled to this ground from the pulse sender circuit. After the relay 3 becomes operated, which removes the ground from the pulse sender circuit, the lockup ground for the operated relay C or D, alone, is passed through the contacts on relay E and the MANSW key to the winding of relay P. The resulting operation of the relay P applies ground to the winding of relay M, which operates and locks operated. The operation 01' the M relay lights the SW lamp; opens the SP (all lamp circuit; and operates and locks operated relay N by paralleling the two relay windings. The operation of the relay N applies operating grounds to the minor ofllce audible alarm and annunciator lamp. The ground applied to the minor audible alarm, and the lock-up ground on the relays M and N are derived separately through normally released contacts on the relays L and B, respectively. Relay P is required to prevent relay M lock-up ground from backing up to the windings oi the relays C and D.

The switch from the working line to the spare line in the manner described will result in the sheet of the working line failure being transferred item the pilot voltmeter switchingrelays associated with a working line to the corresponding pilot voltmeter switching relays associated with a spare line, which will cause the sampling process described above under Spare line failure" to begin.

Simultaneous hit on both lines Simultaneous operation or the working and spare line pilot voltmeter switchim relays causes the operation of the relays G and A. The operation of the relay A, since it is slow to operate, is preceded by the operation of the relay G, which prevents a switch from being caused by the subsequent operation of relay A, by opening the Pulse sender circuit- The operation 01 the relay CorD,duetothereleaseottherelay1-Iwhen relay 0 operates, results in the operation of the pilot voltmeter switching relay reset mechanisms, as described above under Spare lineiailure, up to and including the first reset operation.

No switch or alarm results from the latter oporation. The operation does. however, result in the operation or the relays B, J and K, as described above under "Spars line failure," which sets up the alarm circuit connections so that any continuation o! the working line iaiiure beyond thereleaseoi'theresetoperation willresultin a total i'ail alarm, as will be described below under Total failure.

If the line iailm'es do not continue beyond the release of the reset operation (a total of approximately two seconds elapsed time from the beginning of the line failure), that reset operation will result in the permanent clearance or the pilot voltmeter switching relays, with the subsequent release oi the relays B, J and K, as described above under "Spare line failure."

Total lcilure A total failure results in the simultaneous operation oi the working and spare line pilot voltmeter switching relays. An immediate reset of these relays is then executed, as described above, under Simultaneous hit on both lines."

At the end of the reset period, the relays A, B, CorD,HandJar-eoperated. TherelayJis held operated by a ground applied from the grounded pulse sender circuit, which is transferred by the operated relay B to the winding of the relay J.

Upon the release of the relay A, the charged loo-microrarad section oi condenser C1, which has been connected to the winding ol the relay A, is transferred to the winding of the relay K through operated contacts on relay J. The charge on this transferred condenser passing through the winding of the relay K, operates it, and it locks operated through operated contacts on the relay J.

The release of the relay A also releases the operated relay 0 or D and the associated pilot voltmeter switching relay reset mechanisms. The release 0! the reset mechanisms. permits the working and spare line pilot voltmeter switching relays to operate, applying ground to the working and spare line c leads, respectively.

The operation of the relay K opens the pulse sender circuit back toward the relay A; and reapplies a lock-up ground derived from the relay 1-, toward the relay J, via released contacts on the relay G, and operated contacts on the relay B. Relay J does not release during these operations. due to the condenser Ca (fiil-microfarad) con nected to its winding, the discharge of that con denser through that winding making the hold time or the relay J at least a tenth of a second.

Ground applied to the spare line c2 lead uperates the relay G. The operation 0! the latter relay renews the lock-up mud to the winding oi the relay B; disconnects the 24-volts from the winding of the relay H; applies ground to the winding of the relay A; disconnects the lockup ground trom the winding 0! the relay J; and applies ground to the winding of the relay N through contacts on relay G, causing a 8? tall alarm, as described above under Spare line failure.

The ground applied to the winding of the relay A by the operation oi the relay G operates relay A. This permits the ground previously applied to the working line cl lead to pass through operated contacts on relay 8. and through now operated contacts on relay A to the winding oi the operated relay J to lock that relay operated.

The ground that was previously applied to the working line cl leadhasalreadythrough the 'operated contacts on the relay B, through released contacts on relay R, and through operated contacts on relays J and K, to the winding of the relay L, which operates.

The operation of relay L silences the SP tail alarm by opening the ground to the minor oillce audible alarm circuit; and releases the relay N, if the relay S has not been previously operated, which extinguishes the SP fail lamp and the oillce minor alarm annunciator lamp. It the relay S has been previously operated, relay N remains locked operated to the operated relay 8. The operation of relay L also applies ground to the ofllce major alarm annunciator lamp, and to the oilloe audible major alarm if the relay S is not operated; lights the total i'ail lamp; applies a lock-up ground to its own winding through the same contacts on relays J and K, through which it received its initial operating ground; and applies a, ground directly to the winding of the relay R.

The relay S. which is the alarm control (ACO) relay, obtains its lock-up ground through normal- 1y released contacts on the relay F, through operated contacts on relay B (when that relay is operated), and through paralleled released contacts on the relays N and R. Therefore, it the relay B is operated, and the relay F and either or both the relays N and R are released, relay S may be locked operated.

The application of ground to the winding of relay R, by the operation of the relay L, operates the relay R, which is slow-acting. The operation of the relay R. opens the circuit, between the relays B and J, over which the relay L received its initial operating ground. This does not release relay L, since it has been previously locked operated. In addition, the operation of relay R opens one of the paralleled relay 8 lock-up circuits, applies a ground to the SP fail alarm circuit which has been previously opened by the operation of the relay L, so the relay N is not operated by this ground. The operation of relay R also closes parallel lock-up circuits to its own winding from the relay S, which, it operated, will lock the relay R operated as long as the relay 8 is operated, and from the relay. N which will also look the relay R operated as long as the relay N is released.

If the relay S is operated, and the relay N is locked operated to it, the operation of relay R. opens the last remaining paralleled relay S lockup circuit. This releases the relay S, which, in turn releases the relay N and applies a ground through operated contacts on the relay L to the oflice major audible alarm.

Operation of the relay S will now silence the oilice audible major alarm, and will lock itself operated through released contacts on the relay N, operated contacts on the relay B, and released contacts on the relay F.

The last operation of relay G eventually releases the relay H, which causes a sampling reset as described under Spare line failure." The relays J, K, L and R. remain operated, and the relay S also remains operated, it previously operated to silence the ofiice audible major alarm.

The sampling reset operations continue until the lines are restored to "good" condition, as described under Spare line i'ailure" above.

Upon simultaneous restoration of both lines, and upon the release of the next subsequent reset, both working and spare line pilot voltmeter switching relays are permanently restored to the deenergized condition so that grounds are no longer applied to the corresponding c leads.

At this moment the relays B, H, J, K, L and R. and possibly the relay S, it previously operated to silence the alarm, are operated. A ground through released contacts on the relay E, through operated contacts on the relay K, through released contacts on the relay G, and through operated contacts on relay B to the winding of relay J is holding the latter relay operated, so a total fail alarm is maintained.

Since the relay G does not become operated, the loch-up ground is not again restored to the winding of the relay B. In approximately three seconds, the relay B releases. applying a shortcircuit to the winding of the relay K, which releases immediately, and at the same time disconnects the lock-up ground from the relay J which releases a little later.

The release 01' relay K disconnects the lock-up ground from the relay L, which releases, removing one oi. the lock-up grounds from the relay R, which remains lock-operated through, as yet released contacts on the relay N, and operating contacts on the relay 8, it previously operated.

The release or the relay L also discontinues the total fail alarm and closes the SP iail alarm circuit, This latter action passes the ground applied by the operated relay R to the SP rail alarm circuit on to the winding of the relay N, which operates and locks operated causing an SP fail alarm, which serves as a total failure restoration alarm.

The operation oi the relay N while the relay R is still operated, opens the lock-up ground circuit to the relay 8, and so releases that relay. it operated, and removes a lock-up ground from the relay R.

The release of the relay 8, if it had been previously operated to silence the total fail alarm, removes a last lock-up ground i'rom the winding of the relay R, releasing the latter relay. It the relay 8 had not previously been operated, the relay R eventually releases, after the relay N is operated, due to the release of the relay L.

If the total failure was followed by the restoration of the working line only, the working line pilot voltmeter switching relays are permanently restored to the released condition upon the release of the next subsequent reset. The relay 0 is, however, operated by the subsequent operation of the spare line pilot voltmeter switching relays.

The operation of the relay G restores the lockup ground to the relay B, which holds that relay operated, and disconnects a lock-up ground from the relay J which was derived from the released relay F through operated contacts on the relay K.

Since a ground is not again applied to the working line cl lead, ground is not reapplied to the winding of the relay J upon the operation of the relay A, which would be the case, had the working line pilot voltmeter switching relays operated. After approximately one-tenth of a second, the relay J releases. This opens the lock-up ground circuit to the relay L, which releases that relay, and causes the SP iail alarm to operate. The release of relay J also releases the relay K.

The ensuing SP iaii alarm is now not simply a total failure restoration alarm, but actually represents the existence of such, due to the operation or the relay G, which applies a ground to the winding of relay N as described above under Spare line failure.

If the total failure was followed by the restoration or the spare line only, the spare line pilot voltmeter switching relays are permanently restored upon the released! the next subsequent reset.

The presence or the ground on the working line cl lead as a result or theoperation of the working line pilot voltmeter switching relays does not aflect the circuit. since the relay A'stays released along with the relay G.

As in the case of simultaneous restoration of both lines, the relay B eventually releases, which releases the relays J and K, which in turn releases the relay L, which operates the relay N and eventually releases the relay It, resulting in the operation of the 8? fall alarm, in previously dc;- scribed.

The release of the relay 3 transfers the grounded working line cl lead to the winding of the relay A, which operates. This applies a ground to the pulse sender circuit through now released contacts on the relays K, G, B and J, through contacts on the relay E to the winding of the relay C or D, which causes a switch as described under "Working line failure above. The ensuing operation of the relay P causes the operation of the relay H which extinguishes the SP fall lam and lights the SW lamp.

Failure of working line durino'lailure o! spare line Assume that a sampling reset has been completed, and a spare line failure has caused the operation of the relay G, which has operated the relay A and locked operated the relay B. The relay H has not as yet released. Also assume that the relays J and K have become released from their last pulsed operation, as described above under Spare line failure."

Now assume that the worhng line failure causes the working line pilot voltmeter switching relays to app y round to the working line cl lead. As soon as the relay it becomes operated, due to the previous operation of the relay 6, or ii the relay A has already become operated. ground On the working line ci lead is passed through operated contacts on the relays B and A to the winding of the relay J, which is slow to operate. At the same time, this same ground applied to the winding of the relay J is passed through released contacts on the relay K, through operated contacts on relay G. through contacts on the relay E to the winding of the relay or D, causing an immediate reset.

Upon release of the reset, the renewed ground on the working line cl lead is now passed through released contacts on the relay R, through now operated contacts on the relays J and K to the winding oi the relay L, which results in a total fail alarm, as described above under "Total failure.

If the working line failure occurred during or immediately following a reset operationfso that the ground was applied to the working line cl lead, while the relays J and K were yet operated, an immediate total fail alarm would occur. without an intermediate sampling reset.

Hit on working line during failure of spare line If a hit occurs on the working line after the relays J and K have released, an immediate reset is caused, as described above under Failure of working line during failure of spare line." This reset restores the working line pilot voltmeter switching relays permanently, so the circuit continues to function as described above under Spare line failure," without a total fall alarm. If, however, the hit occurred at the instant of reset release, so that the working line pilot voltmeter switching relays could apply a ground throughyetoperatedrelays-landKtothewinding of the relay 8, an immediate total tail alarm would occur. The resulting total fail alarm, however, would only be maintained through the next subsequent reset. at which time the alarm would again become SP fail as described above under Total failure" (followed by restoration of the working line).

Dasclur'rroil or MAI. Oran-nos Test and alarm cut-oil Operation of the GD-TBT-ACO key operates the relay 8, which applies ground to the WKG REG or WKG ALT lamp via contacts on the relay E. Operation of the relay 8 also disconnects ground from the allies audible alarm circuit and transfers the alarm lock-up o! the relays M and- N to the alarm ground, which is derived through normally released contacts on the relay 8, cperated contacts on the relay B, and operated contacts on the relay 8. The relay 8 looks operated on the same ground, except that its lock-up is derived through parallel released contacts on the relays N and R.

Lock

Operation of the GDTSTACO and lock keys simultaneously passes ground through contacts on the operated GDT8'1ACO and lock keys to the lock lamp and the winding of the relay F, lighting the lock lamp and operating the relay P. The relay F locks operated and the lock lamp is maintained lighted by ground through normally released contacts on the GD-TST-ACO key and the unlock keys in parallel.

The operation of the relay F opens the reset circuit, applies volts through the resistance D to the winding of the relay K, which operates, applies ground through contacts on the relay E to the WKG REG or WKG ALT lamp, which l ghts, applies ground through contacts on the relay E to the winding of the relay 0 or D. which operates. and applies ground to the winding of relay A, which operates.

The operation of the C or D relay, while the relay H is operated, passes a ground from the operated relay H to the winding of the relay B, which operates. With the relays A, B, C, or D and K operated, the circuit is immediately receptve to line failure alarms.

If a spare line failure occurs, the resulting operation of the relay (3 applies a ground through operated contacts on the relay B, through released contacts on the relay L to the winding of the relay N. which operates, and through released contacts on the relay M to the SP fail lamp, which lights. The operation of relay N applies grounds to the allies minor alarm circuit.

The operation of the relay N p the ground applied to its winding through its lock-up contacts to open contacts on relay 8. Operation of relay 8 to silence the alarm, passes this ground through those normally open contacts on the relay 8, through released contacts on relay R to the lock-up contacts on the relay 8. which locks operated that relay. It is therefore seen that the ACO (relay 8) will lock up on a 8? fall alarm, even though the switching circuit is locked by operation .of relay F.

If a working line failure occurs while the switching circuit is locked, the ground applied to the working line at lead is passed through operated contacts on the relay 8. through operated contacts on the relay A to the winding of the relay J, which operates.

When the relay J becomes operated, the ground on the working line cl lead is passed through released contacts on the relay R, through operated contacts on the relays J and K to the winding of the relay L, which operates, resulting in a total fail alarm.

With the relay F operated, the normal S lockup ground circuit is opened, and the operation of the relay L prevents a lock-up ground from being applied to the relay S through contacts on the relay N, as described in the above description of spare line failure while locked. Therefore, it is impossible to lock the ACO (relay S) during a working line failure while the switching circuit is locked.

While the switching circuit is locked by operation of the relay F, the reset circuit is open only at contacts on the operated relay F. perating the unlock key closes a parallel circuit around these open contacts, so a reset results.

Unlock Simultaneous operation of the GDTST-ACO and unlock keys disconnects the lock-up ground from the winding of the relay F, releasing that relay. The operation of the unlock key immediately closes the reset circuit. Upon the release of the relay F, the reset circuit becomes closed at relay F, and the reset continues to operate until the relays A and C or D release.

Manual switch Simultaneous operation of the GD-TST-ACO and MAN SW keys passes a ground through those operated keys, through the released contacts on the relay A, to the pulse sender circuit, which traverses released contacts on the relays K, G, B and J, through contacts on the relay E to the winding of the relay C or D, causing a switch as described under "Working line failure.

When the relay C or D becomes operated, it locks operated on the ground applied to the pulse sender circuit from the operated TST-ACO and MAN SW keys.

Ground is passed through contacts on the relays H and C or D to the winding of the relay B which operates. The relays B and C or D remain operated until the GDTSTACO and MAN SW keys are released. No reset operation occurs since the relay A is not operated.

Conversion of SW alarm to SP jail alarm As described under "Manual switch" above, the simultaneous operation of the GD-TST-ACO and MAN SW keys applies a lock-up ground to the relay C or D. This ground does not, however, cause a switch if the relay B is operated by previous operations of the switching circuit.

When the relay C or D is held continuously operated, reset will occur as rapidly as the relay A can go through its operate and release cycle.

Assuming a spare line failure, the spare line pilot voltmeter switching relays apply a ground to the winding of the relay G, which operates. The operation of relay G applies a ground to the winding of the relay A, which operates. The operation of relay A causes an immediate reset, since the relay C or D is locked operated. The reset immediately releases the relay G, which removes the ground from the winding of the relay A, which releases in approximately two seconds. Upon the release of the relay A, the reset releases which again causes the operation of relay G.

Ordinarily, when the relay C or D is not locked operated, the relays J and K do not both become operated and the relay G released, simultaneously, except when the relay A also released. Exoept under total fail conditions, when the relays J and K are held continuously operated, the

relay K will never be operated at a time when it both the relay G is released and the relay A is operated. The release of the relay A causes the operation of the relay K. This is followed quickly by the operation of relay G, which causes the operation or relay A.

The rapid reset sequence resulting from locking operated the relay C or D results in the relays J and K becoming permanently operated. Usually the relay G stands operated for such a long period, awaiting the release of relay H which results in a reset, that the relays J and K release early in that period. However, with the relay C or D locked operated, a reset follows the operation of the relay G, as soon as the relay A gets operated, which immediately releases the relay G. This short interval that the relay C is operated is insuilicient to release the relay J, which holds operated the relay K.

Now, with the relays A, J and K operated, and the relay G released, ground passes through released contacts on the relay F, operated contacts on the relay K, released contacts on the relay G, operated contacts on the relays B and A, released contacts on the relay R, and operated contacts on the relays J and K to the winding of the relay L, which operates the relay L, causing a total fail alarm, as described under Total failure." The operation of relay L releases the relays M and N which extinguishes the SW alarm lamp, as described under Total failure.

Upon release of the GDTSTACO and MAN SW keys, the sampling rate is reduced to normal, permitting the release of the relays J and K. This releases relay L, which releases the total fail alarm and institutes an SP iail alarm. as described under "Total failure."

Sampling rate Sampling, or automatic periodic switching relay reset operations. is controlled by the relay H, as described under "Spare line failure." The release time of the relay H is controlled by the amount of capacity which is connected to its winding by the operation of a relay B. This capacity is normally a lofl-microrarad section of the C: condenser. which section is shunted with the resistance R1. The charging rate of this condenser section through the series resistances R: and R: and the winding resistance of the relay H is such that approximately six seconds is required irom the time that the relay G operates, which removes a short-circuit from the first C: condenser section and the parallel resistance R1, before the condenser charging current reduces to such a value that the relay H releases. Due to the resistance R1 shunted around that condenser section, the condenser charging current must reduce to approximately .5 milliamperes below the H relay release value before that relay releases.

By operating the slow sampling key, the remaining sections of the C2 condenser totaling 700 microfarads are added to the condenser capacity, which prolongs the charging time to such a value that approximately one minute elapses belore the relay H releases, after the operation of the relay G. A charge is normally maintained on all sections of the C: electrolytic condenser. An associated guard lamp is lighted when the slow sampling key is operated.

Switch alarm hold Prior to operation of the GD-TST-ACO key to silence an alarm by operation of the relay 8, the alarm relays M and N lock up on a ground passed through normally made contacts on the SAH (switch alarm hold) key and through released contacts on the relay 5.

Upon operation of the relay S to silence the alarm, the lock-up for relays M and N is transierred to a trouble ground, as described under Test and alarm cut-oil." If the alarms are not silenced, the transfer of alarm relay lock-up ground will not occur. This will cause the alarm to endure even after the line trouble has cleared, since the relay M or N, or both, will remain locked operated. Operation of the relay 8 will now open this lock-up ground. releasing the relays M and N, which silences the alarm.

If the BAH key is operated, the M and N relay lock-up ground is transferred from solid groimd to the circuit over which the trouble lock-up ground is derived. Then when an alarm occurs, and the relay M or N, or both, become operated, they look operated on the trouble ground only. which is maintained for the duration only of the line trouble. Hence with the BAH key operated, the alarm will endure for only the duration of the line trouble causing that alarm.

The SAH key through its lower contacts operates the line switch and alarm control circuit 180' for the east-to-west direction of transmission in similar manner.

The arrangements of the invention are not limited to systems utilizing two lines, one for a working circuit and the other for a spare circuit, for each direction of transmission, as shown in Fig. 1, but are applicable as well to systems employing three lines, two as working circuits and one as a common spare circuit, for each direction of transmission. It is assumed that in the latter system one working circuit may, if desired, take precedence over the other working circuit to such an extent that the latter circuit may be forfeited, if necessary, to maintain service on the preferred line. It is further assumed that the two working circuits and the spare circuit for each direction of transmission may take any of the six possible permutations on the three lines.

Fig. 3 shows schematically, and in part diagrammatically, the circuit arrangements of the invention applied to adjacent main repeater sections of the two workim; lines for the westto-east direction of transmission in such a system. As shown, there are three identical coaxial lines LC, Li) and LE extending between a switching repeater station A at the input and a switching repeater station 13 at the output of the adjacent switching sections. Each of the lines LC, LD and LE is completely equipped with a transmitting amplifier TA and a receiving amphfler RA, and is assumed to be equipped with the required automatic gain regulating and equalizing apparatus (not shown).

At station A, the terminal coaxial line portions Th1 and 'lLa for the upper repeater section are coupled through balanced windings oi the hybrid repeating coil HCa in conjugate relation with each other and in energy transmitting relationwiththeoutputlinecmoithe switching section (or terminal), so that each portion receives half of the energy of the incoming west-to-east signals from that line. The fid-kilooycle and 2064-kilocycle pilot wave sources PM and Pa: having their combined outputs connected to the net side of the hybrid coil HCA are adapted to supply pilot wave energy of those frequencies through HCA in common to theterminallineportions'l'laand'llaofthe upper repeater section, and to balance the impedance of the incoming line CLA through that hybrid coil.

Similarly, at station A the terminal coaxial line portions TL: and TL; for the lower repeater section are connected in conjugate relation with each other and in energy transmitting relation with the output line CLa of the preceding switching section through balanced windings oi the hybrid repeating coil HCn, so that each terminal lineportionreceiveshalfoithe energy from the output line CLs of the preceding switching section (or terminal). The lid-kiloeycle and 2064-kilocycle pilot wave sources Pm and Pa: having their combined outputs connected to the net side of the hybrid coil HCB, are respectively adapted to supply pilot wave energy of those frequencies through BC}! in common to the inputs of the terminal line portions TL; and Th of the lower repeater section, and to balance the impedance of the incoming line CLn through that hybrid coil.

At station A, the line switching circuits LS1 andlsawiththeirrelaysinthenormalimoperated condition shown, connect the output of terminal line portion TL1 in worlnng relation withtheinputofthecoaxiallinew;theoutput of the terminal line portion TL: in working relation with the input of the coaxial line ID; the output, of the terminal line portion TL: in working relation with the input of the line LE; and the local (n-ohm) terminating resistance TN: across the output oi the terminal line portion Tla so that it balances the impedance 0! the line connected to the output of the terminal line portion T14, through the hybrid coil HCa.

when an operating ground is applied by the local control circuit C01 simultaneously to the relaysAl andalinswitchingdrcuitllsiandthe relaysA3 andAzintheswitching circuitISz. only, those relays operate to disconnect the input of the line LC from the output of 'I'Li and to connect it to the output of Tia; to disconnect the input of line ID from the output of 11a and to connect it to the output of Th1; while maintainingtheeonnectionoftheinputoftheline mtotheoutputof'flaandoitheterminating network TN: to the output of TLl.

When operating ground is applied simultaneouslytotherelayslilandlil inLsiand relaysBI andB3in1S:,only.bythelocalcontroi circuit CCi, these relays will operate to switch the input of the line LE to the output of TL; and the terminating network TN: from the output of TL; to the output of Tie, while maintainingtheinputofthelinellcconnectedto theoutputof'l'inandtheinputotthellnem connected to the output of Tie.

When operating grounds are applied simultaneously from the local control circuit CCi to thewindlnzsofalltherelaysintheswitching circuits LS1 and LS2, these relays will operate to switch the connection of the input of the line LC to the output of T14; the connection of the input of the line LD to the output of Tia; the

input of the line LE to the output of Th, and the terminating network TN: to the output of 'I'Lz.

At the switching repeater station B at the output of the adjacent switching section, shown in Fig. 3, there is a terminal line portion TLs for the upper switching section, which is assumed to connect through a hybrid coil and associated line balancing network (not shown) directly to the next succeeding switching section; a terminal line portion TLe for the lower switching section, which is assumed to connect through a hybrid coil andassociated balancing network (not shown) directly to the next succeeding switching section: and a terminal line portion 'I'Lv terminating in a local balancing network TNa.

At the switching repeater station B, there are three line switching relay circuits LS3, LS4, and LS5, which, with their relays in the normally unoperated condition, connect the output of the line LC in working relation with the input of the next repeater section through line TLs; the output of the line L1) in working relation with the input of the next repeater section through TLe; and the output of the line LE terminated by network TN: through 'I'L-i.

Switching relays Cl and C2 and switchlng relays Cl and C3 in the line switching circuit LS3 are adapted to be operatively energized by operation of the control relays C4 and C5, respectively, when operating grounds are supplied to the respective control relays from the local control circuit C2- Switching relays DI and D2 and switching relays Di and D3 in the line switching circuit LS4 are adapted to be operatively energized by the operation of the control relays D4 and D5, respectively. when operating grounds are respectively applied to the latter control relays from the local control circuit CO2. Similarly, the switching relays El and E2, and El and E3 in the line switching circuit LS5 are adapted to be operatively energized by operation of the control relays E4 and E5, respectively, when operating grounds are applied to these respective control relays from the local control circuit CO2.

The control circuit 061 at the switching repeater station A and the control circuit CC: at the switching repeater station B are controlled to provide the required operating grounds for the line switching circuits at the respective stations to provide any one of the six possible permutations of connections of the lines LC, LD and LE to the switching section terminal line portions TLi to TL-: and the terminating networks 'I'Na and TN::, to insure satisfactory through signal transmission over the repeater sections in spite of line failures in the several lines, from the single automatic line control and alarm circuit VLSCi at station B, similar to the circuit LSC in the system of Fig. 1.

The control alarm circuit LSCi, in turn, is controlled by the 64- and 2064-kilocycle pilot voltmeters PVs and PVe bridged across the terminal line portion 'I'Ls; the 64-kilocycle and 2064-kilocycle pilot voltmeters PV-z and PVs bridged across the terminal line portion TLa; and the 64-kilocycle and 2064-kilocycle pilot voltmeters PVa and PVm bridged across the terminal line portion TLn at the switching repeater station 3. The pilot voltmeters PVs to PVm, which are similar to the corresponding 64- and 2064-kilocycle pilot voltmeters PV1 to PV; in the system of Fig. 1, opcrate in a manner similar to the latter pilot voltmeters as described in connection with Figs. 1

1 1 and 2, in response to abnormal variations in the level of the 64-kilocycle and 2064-kilocycle pilot waves received over the lines to which the associated output line sections are connected at any time, to supply operating ground pulses to the line switching and alarm control circuit LSCi. The latter circuit operates in a manner similar to that described for the similar circuit LSD in connection with Figs. 1 and 2, in response to operation of one or both pilot voltmeters associated with the working lines; to continuously monitor the several lines for line failure conditions (by periodically resetting the switching relays in all pilot voltmeters) when either or both of the pilot voltmeters associated with the working line operate indicating failure or partial failure of that line; to operate appropriate alarm apparatus indicating that failure; and to transmit control pulses over the remote control leads RC1 and RC: to the control circuit (301 at station A and the control circuit CC: at station B to operate those circuits to provide the appropriate grounds to produce the desired one of the above-described switching operations for the line switching circuits LS1 and LS2, and LS: to LS5 at switching stations A and B, respectively.

In the preferred operation of the system of Fig. 3, the switching circuits would be arranged to provide through signal transmission normally over the adjacent switching sections by way of the lines LC and LD, respectively; when line LC only fails to switch through transmission from that line to the line LE if that line is in tolerable working condition as indicated by the unoperated condition of both pilot voltmeters associated with its terminated output line TLv; if the line LD only fails to switch transmission from that line to the line LE if that line has not failed also; if both the working lines LC and LD fail simultaneously to switch through transmission over the switching section from the preferred one of them, say, line LC, only, to the spare line LE if the latter has not failed also; and if any line operating as one of the working lines fails and the particular line which at the time is operating as the "spare line is not in proper working condition, as indicated by an operated condition of one or both of the pilot voltmeters associated with its output, not to do any switching until the trouble condition has been cleared in the latter line.

The arrangements of the invention have been described above as applied to systems employing one or two working lines in each direction of transmission and a single line operating as a spare for the one or two working lines; and to the use of two pilot waves commonly transmitted over each line to control the testing of the lines, to switch from a failed working line to a good" spare line, and to control the operation of approprlate failure alarms in case of abnormal variation level of any one of the pilot waves. It is apparent, however, that if somewhat more elaborate arrangements of relays are used in the switching circuits operating in a manner similar to the relay switching circuits which have been described, they would be adapted for similar use with systems employing more than two working lines and two or more spare lines if that becomes desirable. Also, a greater number of transmitted pilot waves may be used for control, in which case a corresponding number of additional pilot voltmeters respectively selective to a different one of the added pilot waves would be connected across the outputs of the working and spare lines and utilised to control the common line switch and alarm control circuit in a manner similar to that described for the 64- and 2064-kilocycle pilot waves above. I

The advantages of the arrangements of the invention as described above may be summarized as follows:

(1) The control of the alarm and line switching apparatus by any one of a plurality of pilots of different frequencies outside the signal frequency range enables suitable alarm indication and line switching to be attained for line trouble conditions aflecting different portions of the signal frequency range. thus providing better operation under all service conditions;

(2) The multipilot control permits unattended operation:

(3) Full automatic selection of the "good" line is provided for either attended or unattended operation, except when the control apparatus is manually locked;

(4) A line switch will occur if any pilot on the working line falls, but only if both pilots on the spare line are "good";

(5) No patching out is required for routine maintenance, which is limited to that normally used with pilot voltmeters, and during such a routine, control is retained by one of the pilots;

(6) A major total failure alarm occurs, if working and spare lines have failed, even though preceded by minor switch or spare line failure alarms, or if the working line fails while the switching circuit is manually locked;

('7) A relatively small amount of equipment is required for the several functions, as pilot voltmeters and associated switching relays normally necessary to provide other functions are utilized. Furthermore, the automatic control circuit does not require separate amplifier-rectifiers for the switching and alarm controls, and occupies a small amount of space (14 inches of bay space including a 7-inch line switch relay panel):

(8) The circuit may be readily modified to adapt it for a greater number of working lines and spare lines and to any desired number of pilot waves.

Other modifications of the circuits which have been illustrated and described within the spirit and scope of the invention will be apparent to persons skilled in the art.

What is claimed is:

1. In a-wide frequency band signal transmission system, a plurality of signal transmission lines extending between two geographically separated points in said system, at least one of said lines operating normally as a working line to provide through signal transmission between said points and at least one other as a reserve line normally out of service, means to continuously transmit a plurality of pilot waves of different frequencies outside the signal frequency range, over each of said lines and means automatically responsive to abnormal variation in the received level of any one of the pilot waves transmitted over a working line to effectively transfer through signal transmission between said points from that working line to a reserve line but only if the received levels of all of the pilot waves transmitted over the reserve line are within prescribed tolerable limits.

2. In combination in a wide frequency band si nal transmission system, two equivalent transmission lines including amplifying apparatus, extending between two geographically separated points in the system, one of said lines being normalb conditioned as a working line to provide through signal transmission thereover between said points, and the other as a spare line normally out of through service, means to continuously transmit a plurality of pilot waves of different frequencies outside the signal frequency range, over each of said lines, a plurality of control devices connected to the output of each line, respectively operatively responsive to an abnormal change in the received level of a different one of the pilot waves transmitted thereover, indicating serious-line impairment, and switching means automatically responsive to operation of any one of the control devices connected to the line operating as the working line, only if all control devices connected to the spare line are unoperated, to transfer signal transmission between said points from the working line to the spare line, and to operate appropriate alarms for the impaired line or lines.

3. In a wide frequency band signal transmission system, a plurality of tandem-connected main repeater sections, at least one of said sections comprising a plurality of signal transmission lines each including amplifying means, extending between repeater stations at the input and output of the main repeater section, one of said lines normally operating as a working line to provide through signal transmission over the section to the next main repeater section, and another as a spare line normally out of through service, means to continuously transmit a plurality of pilot waves of different frequencies outside the signal frequency range, over each of said lines, a plurality of control devices connected to the output of each line in said one repeater section, respectively selectively controlled by a different one of the received pilot waves, and operatively responsive only when the received level thereof deviates more than a predetermined amount from normal level in either direction indicating partial or complete line failure, and switching means automatically responsive to operation of any one of the control devices connected to the working line, but only if all the control devices connected to the spare line are unoperated at the time, to switch effectively through signal transmission from said Working line to said spare line, and to provide alarms indicating the line or lines which have failed.

4. In a wide band signal transmission system, a plurality of tandem-connected repeater sections connected between the terminals of the system, at least one of said sections comprising a plurality of equivalent transmission lines having their inputs connected in transmission relation with the output of the preceding repeater section or terminal, extending between the repeater stations at the input and output of the section, the output of one of said lines being normally connected to the succeeding repeater section or terminal so that it acts as a working line to provide through signal transmission from said preceding repeater section or terminal to said succeeding repeater section or terminal, and another of said transmission lines operating as a spare line having a suitable line termination connected to its output end, means to transmit a plurality of pilot waves of different frequencies outside the signal frequency range over each of said lines, means at the output repeater station for selecting from the output of each line and rectifying a different one of the received pilot waves, separate relay means respectively controlled by the rectified pilot waves of each frequency and operatively responsive to a deviation in their received amplitude levels beyond prescribed tolerable limits, eating serious line impairment in the ciated line. switching means at said output repeater station automatically responsive to operation of any one of said relay means controlled from the line operating as the working line, only if all said relay means controlled from the line operating as the spare line are unoperated, to disconnect the output of said one line from said succeeding repeater section or terminal and to connect the output of said other line thereto so as to effectivel switch through signal transmission from the working line to the spare line, and to switch the termination from the output of said other line to the output of said one line, and means responsive to operation of one or more of the relay means controlled from the working line or spare line to continuously monitor or test both lines to determine if an impaired condition exists.

5. In a wid frequency band signal transmission system, a plurality of tandem-connected repeater sections, certain of said repeater sections comprising a regular line normally operating as a workin line to provide through signal transmission to the succeeding repeater section, and an equivalent alternate line normally disconnected from said succeeding repeater section, means to continuously transmit over both of said lines a plurality of equivalent pilot waves of different frequencies outside the signal frequency range, a plurality of control devices bridged across the output of each line, respectively operatively responsive to excessive deviation in the received levels of a different one of the applied pilot waves, caused by complete or partial failure of the associated line, and switching means automatically responsive to operation of any one of the control devices connected to the line operating as a Working line, only if all of the control devices connected to the alternate line are unoperated, to transfer through signal transmission from the working line to the alternate line, to cause continuous monitoring or testing of the working and alternate lines to determin if a failure condition exists, and if a failure condition exists to switch lines if necessary to restore transmission, to cause automatic periodic sampling of the working and alternate lines to determine if a failure condition continues until the trouble causing the failure is cleared, and to operate appropriate alarms indicating the failed condition of any line or lines.

6. The system of claim 5, in which said periodic sampling of said working and alternate lines is attained by causing periodic resettings of said control devices to the unoperated condition.

7. The system of claim in which said switching means comprise a chain of relays with associated timing arrangements determining the rate of sampling.

8. In a wide frequency band repeatered signal transmission system, a plurality of sections of transmission line extending between certain repeater points and embracing at least one repeater span, one of said line sections being normally conditioned as a. working line to provide through signal transmission thereover between a preceding terminal station or repeater span and a following terminal station or repeater span, and another as a spare line normally disabled for such through signal transmission, means to continuously transmit a plurality of pilot waves of different frequencies outside the signal frequency range over each of said lines, a plurality of individual control devices associated with the output of each line, respectively selectively controlled by a different one of the received pilot waves and operating in response to abnormal variations in its received amplitude level, such as would be caused by an intolerable partial or complete failure of the line over which it is transmitted, and switching means energized by operation of any one 01' said control devices, and automatically operating to effectively test both of said lines periodically for such failure conditions during the period of operation of one or more of the control devices; to interpret such conditions in either line and to operate corresponding failure alarms; and to condition said other line as the working line and said one line as the disabled spare line only during the period of operation of one or more of the control devices associated with said one line indicating partial or complete failure thereof, and the simultaneous non-operation of all said control devices associated with said other line indicating a. tolerable operating condition thereof.

9. The system of claim 8, in which said switching means operates to test both of said lines by periodically restoring all 01' said control devices to the unoperated condition to enable operated alarms indicating failure of a line or lines associated with one or more of said devices to be restored to the unoperated condition and then to return to the operated condition if the line trouble condition causing the alarm has not been remedied or to remain unoperated if the line trouble condition no longer exists. a

10. The system of claim 8 in which each of said individual control devices associated with each line comprises an amplifier-rectifier tuned to the frequency of a diflerent one of said pilot waves and a relay having an operating coil energized by the rectified output thereof and a restoring coll, said relay being adapted for operation in response to a predetermined rise or fall in the amplitude oi the supplied energization current from normal value, said switching means operating to test both of said lines by periodically supplying operating grounds to the restoring coils of all of said relays in response to operation of any one of the relays.

11. The system of claim 8 in which said switch ing means comprises a chain of relays operating in sequence in response to operating grounds applied to the first relay in the chain by operation or the control devices associated with the working and spare lines, respectively, said relays having associated timing circuits the constants of which determine the rate of testing of said lines, the operation of the final relay in the chain causing the switch from a working line to a spare line, and the application of an operating ground to the relay chain in response to operation 01' one or more of the control devices associated with the spare line while an operating ground is applied to the chain by operation of one or more of the control devices associated with the working line, preventing operation of said final relay to switch said lines.

12. The system of claim 8 in which the inputs of both of said lines are permanently connected in conjugate relation with each other and in energy transmitting relation with the output of said preceding terminal station or repeater span, a plurality of relays in their normal unoperated condition connect the output of said one line in working relation with the input of the following terminal station or repeater span, and maintain the output of said other line disconnected from said following terminal station or repeater span,

and complete operation of said switching means in response to operation of one or more of the control devices associated with the working line causes operation of said relays to connect the output of said other line to said following terminal station or repeater span and to disconnect the output of said one line therefrom and connect it to a terminating resistance.

13. In a wide frequency band repeatered signal transmission system, three sections of signal transmission line extending between certain repeater points embracing one or more repeater spans, two of said line sections being normally conditioned as working lines to provide separate through signal transmission paths to separate following sections of transmission line. and the third as a spare line normally disconnected from said following sections of transmission line, means to continuously transmit a plurality of pilot waves of diflerent frequencies outside the signal frequency range, over each of said three line sections, a plurality of control devices respectively selective to a different one of said pilot waves, bridged across the output of each of said three line sections, each operatively responsive only to a predetermined deviation in the received amplitude level of the selected pilot wave such as would be caused by serious impairment in the associated line, and switching means automatically responsive during operation of any one of said control devices to continuously monitor each of said three line sections to determine if an impaired condition exists, and to periodically test the lines as long as a failure endures; to provide appropriate alarms indicating the impaired condition of any line sections; and to effectively substitute said spare line as a working line in place of a working line which has become impaired only if said spare line is in tolerable working condition.

14. In a signal transmission system of wide frequency range, a plurality of equivalent transmission lines extending between an incoming line and an outgoing line. at least one of which is normally conditioned as a workin line to provide through signal transmission thereover between said incoming and outgoing lines, means automatically responsive to a tr failure condition in any frequency range within said wide frequency range in any one of said equivalent lilies to test all of them for transmission failure conditions, and to automatically switch through transmission from the working to the spare line only if the test indicates a failure condition in the working line and a nonfaiiure condition in the spare line.

15. In a signal transmission system of wide frequency range, a plurality of equivalent transmission lines extending from an incoming line to an outgoing line, one normally conditioned as a working line to provide through signal transmission thereover between said incoming and outgoing lines and another as an operative spare line in transmission relation with said incoming line but disconnected from said outgoing line,

aavaoce manual mean for switching through signal on can said incoming and outgoing lines K- normal working line to the normal spare means automatically responsive to a on failure condition in any frequency range within said wide range, in any one of said equivalent lines to test each of them for a failure condition, and to automatically switch ton from a working line indicated by the test as having failed to a spare line only if the test indicates the latter line as being in a non-failure condition, while permitting manual switching between said equivalent lines even though the test indicates both working and spare lines have failed, so as to enable the better of them to be selected for through 16. In a signal ton system of wide frequency range. a plurality of equivalent transmission lines extending between a preceding and a succeeding line section, one being normally conditioned as a working line to provide through signal on thereover between said line sections and another as an operative spare line in on relation with said preceding line section only and terminated in its output, switching means automatically responsive to a transmission failure condition in any frequency range within said wide band in any one of said equivalent lines to continuously monitor all of them at predetermined intervals for transmission failure conditions; to automatically switch through transmission from a working line to a spare line when the monitoring indicates a ton failure on a working line only, to indicate the restoration of any line to a tolerable operation condition and then to restore said switching means to the continuous monitoring condition.

1'7. In a signal transmission system comprising an incoming line, an outgoing line, two or more equivalent transmission lines extending between said incoming line and said outgoing line. one of which is normally conditioned as a working line to provide through signal transmission between said incoming and outgoing lines, and another as an operative spare line in transmission relation with said incoming line but effectively disconnected from said outgoing line, a switching circuit automatically responsive to a tron failure condition in any one of said equivalent lines to switch through transmission from a working line indicated by the test as having failed to a spare line only if the latter is found in tolerable operating condition by the test, and to provide alarms indicating a failed condition of any of the lines, and manual means for looking and unlocking said switching circuit so that while it is locked line switching cannot be performed, whereas the operation of alarms to indicate line failure conditions to an attendant is permitted to enable him to unlock the switching circuit if he so desires.

BIRNEY DYSART. 

